g.c

/*
 * getgrnam_r() implementation for Android NDK
 *
 * Copyright (c) 2015 may safely be consumed by a BSD or GPL license.
 * Written by:   Vladimir Oleynik <[email protected]>
 *
 */

#include <sys/types.h>
#include <grp.h>
#include <string.h>
#include <errno.h>

static size_t add_aligned(size_t sz)
{
    if((sz & (sizeof(char *) - 1)) == 0)
	return sz;
    sz |= sizeof(char *) - 1;
    return sz + 1;
}

static size_t gav(const char *val)
{
    if(val != NULL)
	return add_aligned(strlen(val) + 1);
    return 0;
}

static void *set_field(char **pf, const char *val, char *buf)
{
    if(val != NULL) {
	size_t sz = strlen(val) + 1;
	return memcpy(*pf = buf, val, sz) + add_aligned(sz);
    } else {
	*pf = NULL;
	return buf;
    }
}

int getgrnam_r(const char *name, struct group *grp,
		 char *buf, size_t buflen, struct group **result)
{
    size_t real_sz;
    struct group *r, *g = getgrnam(name);
    char    **gm;
    void *v;
    int membr;

    if(g == NULL)
	return -1;

    real_sz = sizeof(struct group) + gav(g->gr_name) + gav(g->gr_passwd);
    membr = 0;
    if(g->gr_mem != NULL) {
	for(gm = g->gr_mem; ; gm++) {
	    size_t sz1 = gav(*gm);
	    membr++;    /* need NULL always */
	    if(sz1 == 0)
		break;
	    real_sz += sz1;
	}
	real_sz += membr * sizeof(char *);
    }
    if(real_sz > buflen) {
	errno = ERANGE;
	return -1;
    }

    r = v = buf;
    v = set_field(&r->gr_name, g->gr_name, (char *)(r + 1));
    v = set_field(&r->gr_passwd, g->gr_passwd, v);
    r->gr_gid = g->gr_gid;

    if(g->gr_mem != NULL) {
	r->gr_mem = v;
	v = ((char *)v) + (membr * sizeof(char *));
	for(membr = 0, gm = g->gr_mem; ; gm++, membr++) {
		void *v2;
		if((v2 = set_field(&r->gr_mem[membr], *gm, v)) == v)
		    break;
		v = v2;
	}
    } else {
	r->gr_mem = NULL;
    }

    *result = memcpy(grp, r, sizeof(struct group));
    return 0;
}


#ifdef TEST

#include <stdio.h>

int main(int argc, char **argv)
{
    struct group g, *r;
    char buf[1024];
    char **gm;
    int m = 0;

    if(argc != 2) {
	printf("Usage: %s group\n", argv[0]);
	return 2;
    }
    if(getgrnam_r(argv[1], &g, buf, sizeof(buf), &r) != 0) {
	perror("getgrnam_r");
	return 1;
    }
    printf("group = %s\n", g.gr_name);
    printf("group_pass = %s\n", g.gr_passwd);
    for(gm = r->gr_mem; *gm != NULL; gm++) {
	printf("member[%d] = %s\n", m, *gm);
	m++;
    }
    return 0;
}
#endif